A tool holder having a cutting insert assembly at one end thereof generally is provided with a tapered shank which is insertable into a tool block. The tool block is secured to a machine tool which rotates the tool block against a static workpiece or the workpiece is moved while the tool block is maintained in a static position (i.e. non-rotational).
Significant radial and tangential forces act on the cutting insert during machining operations. If the cutting insert is misaligned with respect to the cutting tool and/or if the tool holder is not precisely locked in place in the tool block, tool failure and imprecise cuts result.
In order to provide precise machining of the workpiece, especially for static tool blocks it is essential that the tool holder and tool block are locked together in alignment within narrow tolerances. The locking mechanism typically comprises providing the outer surfaces of the tool holder and tool block with opposed slots or keyways and providing the tool block with projections or keys of complimentary shape which are securable in the slots of the tool holder when the tool holder is operatively secured within the tool block. The key/keyway assembly is used in static tools to both locate the tool holder with respect to the tool block and also to dissipate the extreme torque applied to static tools from a rapidly moving (e.g. rotating) workpiece.
The keys or projections are secured to the base of the tool block slots and extend outward from the tool block slots and into the corresponding slots of the tool holder. The tool holder and tool block are thereby prevented from rotational movement with respect to each other by the contact of the walls of the keys against the walls of the respective tool holder and tool block slots.
The slots of the tool holder and the tool block are located such that the centerline of the locked tool components passes through the center of the aligned pairs of slots. The object is to ensure that the plane passing through the cutting edge of the cutting insert at the end of the tool holder is aligned in a plane corresponding to the centerline of the tool assembly.
This system, however, does not achieve the desired degree of alignment especially for making fine cuts in a workpiece. Industry standards require that the width of a typical tool holder slot of, for example, 0.645 inches, be machined at tolerances of .+-.0.010 inches. Thus, the slot can have a width in the range of 0.635 to 0.655 inches. Since the centerline of the locked tool components is defined by the plane passing through the center of the slot, the centerline may vary for each tool assembly produced because of variations in the width of the slots. This can result in misalignment of the cutting insert and inaccurate cuts in the workpiece.
Furthermore, because the cutting insert is further from the centerline than the tool holder slot, a small displacement in the width of the slot provides an even larger displacement of the cutting insert.
A further disadvantage of center slot alignment is that the keys secured within the slots may not rest flush against the walls of the slot due to the same variations in the width of the slot. Thus, the keys may move within the slot when subjected to the torque applied by the rotating workpieces during machining operations.
It is therefore an object of the present invention to provide a tool assembly which allows precisely controlled center height alignment of the tool components and the cutting insert.
It is a further object of the invention to provide a tool assembly having a centerline which is keyed on a dimension of the tool assembly which is not subject to variation in manufacturing operations.
It is still a further object of the invention to provide a locking mechanism for locking a tool holder to a tool block which locates and locks the tool components together in precise centerline alignment with the cutting insert.